Electrochemical removal of phenol in alkaline solution. Contribution of the anodic polymerization on different electrode materials

Abstract

The removal of organic pollutants based on electropolymerization on an anode was performed in the case of phenol in alkaline solution. The polymer formed by a process involving less than two electrons per molecule of phenol, is then precipitated by decreasing the pH and finally filtered and disposed. The electrochemical polymerization of phenol (C0 = 0.105M) in alkaline solution (pH = 13) at 86 ◦C has been studied by galvanostatic electrolysis, using a range of anode materials characterized by different O2-overpotentials (IrO2, Pt and B-PbO2). Measurements of total organic carbon and HPLC have been used to follow phenol oxidation; the morphology of the polymer deposited on the electrode surface has been examined by SEM. Experimental data indicate that phenol concentration decreases by oxidation according to a first order reaction suggesting a mass transport limitation process. Polymeric films formed in alkaline solution did not cause the complete deactivation of the anodes. SEM results show that the polymeric films formed on Ti/IrO2 and Pt anodes cannot be mineralized. On the other hand, complex oxidation reactions leading to the partial incineration of polymeric materials can take place on the Ta/B-PbO2 surface due to electrogenerated HO• radicals which have an oxidizing power much higher than that of intermediaries formed respectively on IrO2 and Pt. It is assumed that the polymer films formed on these anodes have different permeability characteristics which determine the rate of mass transfer of the phenol. The fractions of phenol converted in polymers were 25, 32 and 39% respectively with Ti/IrO2, Pt and Ta/B-PbO2, a series of materials in which the O2-overvoltage increases.